Conventional gas turbine engines typically include fan, compressor, and turbine rotors each including a plurality of circumferentially spaced blades extending radially outwardly from a rotor disc. The blades typically have either axial entry or circumferential entry dovetails which are disposed in complementary dovetail slots formed in the perimeter of the rotor disc for securing the blades to the disc.
During operation of the engine, the rotor blades are subject to vibratory excitation forces due to, for example, the rotational speed of the rotor and aerodynamic pressure forces from the fluids channeled over the blades. Where the frequency of excitation is the same as one of the resonant natural frequencies of the blades, undesirable resonance of the blades may occur unless suitable damping is provided. For example, in the dovetail-bladed rotor disc described above, some frictional dampening occurs between the dovetails and the rotor discs. Additional dampening may be obtained by providing conventional dampers near the blade roots, the blade mid-spans, or the blade tips. Such conventional dampers may be readily provided since each of the blades is independently manufactured and assembled into the rotor disc.
However, providing effective damping of a gas turbine engine rotor in the form of a blisk presents additional problems. A blisk is an integral bladed-disc assembly wherein the blades are conventionally formed as integral portions of the rotor disc, and are not, therefore, independently manufactured separately from the rotor disc. Nor do the blisk blades have conventional dovetails for being inserted into and removed from the rotor disc. Accordingly, blisks are inherently stiff structures which do not enjoy the type of internal damping which is provided by conventional bladed-disc assemblies. Furthermore, since a blisk is typically manufactured from a single rotor blank with the individual blisk blades being machined therefrom, it is typically not possible to employ conventional dampers therein of the type which are conventionally manufactured for individual dovetailed blades before being assembled to the disc.